Misc cleanup on performance branch

Summary:

Did some trivial stuffs:

* Add more comments;
* fix compiler's warning messages (uninitialized variables).
* etc

Test Plan:

make check

build_tools/format-diff.sh

@@ -47,7 +47,6 @@ fi
 #     ln -s `git rev-parse --show-toplevel`/build_tools/format-diff.sh $PRE_COMMIT_SCRIPT_PATH
 #   fi
 # fi
-
 set -e
 
 uncommitted_code=`git diff HEAD`
@@ -55,7 +54,6 @@ uncommitted_code=`git diff HEAD`
 # If there's no uncommitted changes, we assume user are doing post-commit
 # format check, in which case we'll check the modified lines from latest commit.
 # Otherwise, we'll check format of the uncommitted code only.
-format_last_commit=0
 if [ -z "$uncommitted_code" ]
 then
   # Check the format of last commit

db/memtable.cc

@@ -232,7 +232,7 @@ bool MemTable::Get(const LookupKey& key, std::string* value, Status* s,
     // sequence number since the Seek() call above should have skipped
     // all entries with overly large sequence numbers.
     const char* entry = iter->key();
-    uint32_t key_length;
+    uint32_t key_length = 0;
     const char* key_ptr = GetVarint32Ptr(entry, entry + 5, &key_length);
     if (comparator_.comparator.user_comparator()->Compare(
         Slice(key_ptr, key_length - 8), key.user_key()) == 0) {
@@ -337,7 +337,7 @@ void MemTable::Update(SequenceNumber seq,
     // sequence number since the Seek() call above should have skipped
     // all entries with overly large sequence numbers.
     const char* entry = iter->key();
-    uint32_t key_length;
+    uint32_t key_length = 0;
     const char* key_ptr = GetVarint32Ptr(entry, entry + 5, &key_length);
     if (comparator_.comparator.user_comparator()->Compare(
         Slice(key_ptr, key_length - 8), lkey.user_key()) == 0) {
@@ -401,7 +401,7 @@ bool MemTable::UpdateCallback(SequenceNumber seq,
     // sequence number since the Seek() call above should have skipped
     // all entries with overly large sequence numbers.
     const char* entry = iter->key();
-    uint32_t key_length;
+    uint32_t key_length = 0;
     const char* key_ptr = GetVarint32Ptr(entry, entry + 5, &key_length);
     if (comparator_.comparator.user_comparator()->Compare(
         Slice(key_ptr, key_length - 8), lkey.user_key()) == 0) {
@@ -466,7 +466,7 @@ size_t MemTable::CountSuccessiveMergeEntries(const LookupKey& key) {
 
   for (; iter->Valid(); iter->Next()) {
     const char* entry = iter->key();
-    uint32_t key_length;
+    uint32_t key_length = 0;
     const char* iter_key_ptr = GetVarint32Ptr(entry, entry + 5, &key_length);
     if (!comparator_.comparator.user_comparator()->Compare(
         Slice(iter_key_ptr, key_length - 8), key.user_key()) == 0) {

table/plain_table_reader.cc

@@ -405,7 +405,7 @@ Status PlainTableReader::GetOffset(const Slice& target, const Slice& prefix,
   uint64_t prefix_index_offset = bucket_value ^ kSubIndexMask;
 
   const char* index_ptr = sub_index_ + prefix_index_offset;
-  uint32_t upper_bound;
+  uint32_t upper_bound = 0;
   const uint32_t* base_ptr = (const uint32_t*) GetVarint32Ptr(index_ptr,
                                                               index_ptr + 4,
                                                               &upper_bound);
@@ -464,17 +464,17 @@ bool PlainTableReader::MayHavePrefix(uint32_t hash) {
 
 Status PlainTableReader::ReadKey(const char* row_ptr, Slice* key,
                                  size_t& bytes_read) {
-  const char* key_ptr;
+  const char* key_ptr = nullptr;
   bytes_read = 0;
-  size_t internal_key_size;
+  size_t internal_key_size = 0;
   if (IsFixedLength()) {
     internal_key_size = GetFixedInternalKeyLength();
     key_ptr = row_ptr;
   } else {
-    uint32_t key_size;
+    uint32_t key_size = 0;
     key_ptr = GetVarint32Ptr(row_ptr, file_data_.data() + data_end_offset_,
                              &key_size);
-    internal_key_size = (size_t) key_size;
+    internal_key_size = (size_t)key_size;
     bytes_read = key_ptr - row_ptr;
   }
   if (row_ptr + internal_key_size >= file_data_.data() + data_end_offset_) {

util/coding_test.cc

@@ -41,7 +41,7 @@ TEST(Coding, Fixed64) {
   const char* p = s.data();
   for (int power = 0; power <= 63; power++) {
     uint64_t v = static_cast<uint64_t>(1) << power;
-    uint64_t actual;
+    uint64_t actual = 0;
     actual = DecodeFixed64(p);
     ASSERT_EQ(v-1, actual);
     p += sizeof(uint64_t);
@@ -90,7 +90,7 @@ TEST(Coding, Varint32) {
   const char* limit = p + s.size();
   for (uint32_t i = 0; i < (32 * 32); i++) {
     uint32_t expected = (i / 32) << (i % 32);
-    uint32_t actual;
+    uint32_t actual = 0;
     const char* start = p;
     p = GetVarint32Ptr(p, limit, &actual);
     ASSERT_TRUE(p != nullptr);
@@ -125,7 +125,7 @@ TEST(Coding, Varint64) {
   const char* limit = p + s.size();
   for (unsigned int i = 0; i < values.size(); i++) {
     ASSERT_TRUE(p < limit);
-    uint64_t actual;
+    uint64_t actual = 0;
     const char* start = p;
     p = GetVarint64Ptr(p, limit, &actual);
     ASSERT_TRUE(p != nullptr);

util/dynamic_bloom.h

@@ -23,16 +23,16 @@ class DynamicBloom {
 
   explicit DynamicBloom(uint32_t total_bits, uint32_t num_probes = 6);
 
-  // Assuming single threaded access to Add
-  void Add(const Slice& key) { AddHash(hash_func_(key)); }
+  // Assuming single threaded access to this function.
+  void Add(const Slice& key);
 
-  // Assuming single threaded access to Add
+  // Assuming single threaded access to this function.
   void AddHash(uint32_t hash);
 
-  // Multithreaded access to MayContain is OK
+  // Multithreaded access to this function is OK
   bool MayContain(const Slice& key);
 
-  // Multithreaded access to MayContain is OK
+  // Multithreaded access to this function is OK
   bool MayContainHash(uint32_t hash);
 
  private:
@@ -42,6 +42,8 @@ class DynamicBloom {
   std::unique_ptr<unsigned char[]> data_;
 };
 
+inline void DynamicBloom::Add(const Slice& key) { AddHash(hash_func_(key)); }
+
 inline bool DynamicBloom::MayContain(const Slice& key) {
   return (MayContainHash(hash_func_(key)));
 }